Tailoring phase formation and mechanical properties of low-temperature-grown Al-rich CrAlWN films by selective metal-ion bombardment during high-power impulse magnetron sputtering

Conventional physical vapor deposition of CrAlN coatings on carbon-rich steels (e.g., 100Cr6) is restricted to <∼160 °C to preclude processes deleterious to the mechanical properties of steel. Here, we present a two-step pulsed substrate-biasing strategy in reactive high-power impulse magnetron sputtering to deposit Al-rich, single-phase cubic Cr 1−x−y Al x W y N (x > 0.5, 0 < y < 0.24) films under <∼160 °C. Pulsed substrate biasing favors selective Al⁺ ion bombardment during early stages of film growth (< 200 nm) and subsequently enables Al⁺ and Cr⁺ bombardment by extending the bias pulse width. This approach stabilizes rocksalt CrAlN by suppressing phase separation without interrupting the deposition process. The resultant films are dense, exhibit ∼ 30 GPa indentation hardness, and high residual compressive stress of 4.2 GPa. Introducing W + ions with Cr + and Al + at ion energies of ∼ 30–100 eV lowers compressive stress by up to 0.97 GPa while retaining high hardness and increased film density. These attributes cannot be realized by conventional direct current magnetron sputtering at 500 °C. Such W alloying combined with two-step substrate biasing do not induce grain coarsening and strain relaxation due to tempering in 100Cr6 substrates. This can be adapted for growing low-temperature nitride films on temperature-sensitive substrates.